This invention relates generally to gas turbine engines and more particularly to repairing and/or upgrading certain components used in such engines.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and ignited for generating hot combustion gases. These gases flow downstream to one or more turbine stages that extract energy therefrom to power the compressor and provide useful work. Each turbine stage commonly includes a stationary turbine nozzle followed in turn by a turbine rotor. The turbine rotor comprises a row of rotor blades (sometimes referred to as buckets) mounted to the perimeter of a rotor disk that rotates about the centerline axis of the engine. The nozzle, which channels combustion gases into the turbine rotor in such a manner that the turbine rotor can do work, includes a plurality of circumferentially spaced apart vanes radially aligned with the rotor blades. Turbine nozzles are typically segmented around the circumference thereof to accommodate thermal expansion. Each nozzle segment has one or more nozzle vanes disposed between inner and outer bands that define the radial flowpath boundaries for the hot combustion gases flowing through the nozzle.
The turbine section is mounted at the exit of the combustor and is therefore exposed to extremely high temperature combustion gases. To protect turbine components from the hot combustion gases, they are often cooled with a cooling medium. One common approach to cooling turbine airfoil components (e.g., rotor blades and nozzle vanes) is to bleed a portion of the compressed air from the compressor and direct the bleed air to internal passages in the components. The air circulates through the internal passages to remove heat from the component structure. The air can exit through small film cooling holes formed in the airfoil surface so as to produce a thin layer, or film, of cooling air on the surface. Film cooling can also be used for the inner and outer bands. In this case, a band includes film cooling holes extending radially therethrough. Cooling air passes through the film cooling holes to form a cooling air film on the hot side of the band. Other known cooling approaches include using steam from a combined cycle bottoming engine as the cooling medium for the gas turbine components in a closed-circuit mode. A separate off-board compressed air system delivering closed-circuit cooling air to turbine components has also been employed.
Currently, cooled gas turbine components, such as rotor blades and nozzle segments, are typically fabricated from investment castings. Cast components include the major design features of the cooling scheme (such as passage size and routing and the location and size of features like internal rib turbulators) within their casting definition. Therefore, changing the cooling scheme would require a redesign of the investment casting, which involves significant time and cost.
As cooled turbine components are exposed to severe conditions during engine operation, it is sometimes discovered that certain local regions are inadequately cooled for the intended function or life of the component. This can result in distress such as burning, cracking and the like in the local region. Such distress will lead to premature service or reduced life for the component. Often, modifying the component""s cooling scheme can alleviate local distress. However, as mentioned above, such modification ordinarily requires an expensive and time consuming redesign of the investment casting. Accordingly, it would be desirable to have a method for modifying the component cooling scheme so as to improve local cooling without going through the lengthy and costly development cycle of redesigning the investment casting.
The above-mentioned need is met by the present invention, which provides a method of modifying a gas turbine engine component having a cooling medium source associated therewith. The method includes forming at least one channel in the component such that the channel is in fluid communication with the cooling medium source. Then partially filling the channel with a removable material and covering the removable material with a patch material so as to completely fill the channel. Lastly, the removable material is removed from the channel so as to create an internal cooling passage in the component.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.